Guidelines for imaging the choriocapillaris using OCT angiography.

PURPOSE To provide guidance on how to appropriately quantitate various choriocapillaris (CC) parameters with optical coherence tomography angiography (OCTA). DESIGN Evidence-based perspective. METHODS Review of literature and experience of authors. RESULTS Accurate and reliable quantification of the CC using OCTA requires that the CC can be visualized and that the measurements of various CC parameters are validated. For accurate visualization, the selected CC slab must be physiologically sound, must produce images consistent with histology, and must yield qualitatively similar images when viewing repeats of the same scan or scans of different sizes. For accurate quantification, the measured inter-capillary distances (ICDs) should be consistent with known measurements using histology and adaptive optics/OCTA, the selected CC parameters must be physiologically and physically meaningful based on the resolution of the instrument and the density of the scans, the selected algorithm for CC binarization must be appropriate and generate meaningful results, and the CC measurements calculated from multiple scans of the same and different sizes should be quantitatively similar. If the Phansalkar's local thresholding method is used, then its parameters must be optimized for the CC based on the OCTA instrument and scan patterns used. It is recommended that the window radius used in the Phansalkar method should be related to the expected average ICD in normal eyes. CONCLUSIONS Quantitative analysis of the CC using commercially available OCTA instruments is complicated and researchers need to tailor their strategies based on the instrument, scan patterns, anatomy, and thresholding strategies to achieve accurate and reliable measurements.